In co-transcriptional capping, cap analogues are added directly to the IVT. Although this method is simpler than the enzymatic capping, the drawback is the elongation in the wrong direction. The addition of anti-reverse cap analogues (ARCA) that contains an additional 3’-O-methyl group on the m7G ensures the elongation of the mRNA will occur exclusively at the correct orientation, which will result in higher translational activity compared with the traditional cap structure.